For every dunning letter there will be some time gap.

for example we have 3 dunning letters

dlettername days

dun1 1

dun2 2

dun3 3

If we ran this request 3 times, fourth time if you run the report there will
be no output, because all the 3 letters we have already ran.

If you want to change the days means you need to go to ar responsibility and in
dunning letterset you need to change the days for the dunning letters.

navigation:print->dunning letter set